Add LitteThings to that list of under-the-radar viral giants. The site’s traffic has exploded from 8 million uniques in November to nearly 40 million in May, thanks in large part to Facebook, where it has 1.6 million likes (80 percent of the site’s traffic comes from social). Quantcast says the site is the 23rd-largest site in the U.S, above even LinkedIn and FoxNews.com. Its formula for success: an exclusive focus on positive, uplifting content for its predominantly female readership — told with an Upworthy-esque flair for the sensational and hyperbolic.

The site’s metabolism is necessarily speedy. The LittleThings 30-person editorial team posts upwards of 50 articles each day and is trying to push that post count above 60 in the next few months. That’s doable, considering that the site’s content is an aggregated mix of photos and video uploaded elsewhere, particularly YouTube.

“We look at the traffic, and it validates what many of us know and feel, which is that people really want this sort of positive news,” said Little Things’ chief operating officer Gretchen Tibbits. “The more people we get to smile, the more we can get them to read and engage and share with their friends.”

Tibbits, whose resume includes executive spots at Maxim, ESPN and Hearst, lends some cachet to LittleThings’ brand, which has remained a relative unknown despite its extensive reach. The site is actually a spin-off of pet-supply site PetFlow, which launched a viral pet blog last January and realized it could be a viable business in its own right.

The playbook for viral publishing is pretty established by this point: Build a massive audience on top of Facebook, then once you reach a critical mass, monetize that audience either through display advertising, sponsored content or some sort of traffic trading deal. LittleThings has a hand in all three of those monetization streams. On the sponsored-content side, it says it offers the ultimate “brand-safe environment.” It ran a sponsored-content deal with Ford back in May, for example.

But being a viral publisher these days is a mixed bag. Facebook hasn’t been shy about tweaking its algorithm to clamp down on content that it thinks hurts its users’ experience. The result for sites like Upworthy, Distractify and ViralNova is an incredibly bumpy traffic picture from month to month, particularly over the last year.

ViralNova’s traffic, for example, climbed to 38 million uniques last September before sinking to 16.8 million just three months later. Distractify climbed to 18.7 million monthly uniques before its steady plunge last September. It hasn’t recovered. Upworthy, for its part, has decided to pivot toward producing original content.

Tibbits said LitteThings is looking for ways to Facebook-proof its traffic by investigating in other platforms and also putting more effort into original content. The site might also be insulated by the intense engagement of its readership. Roughly 45 percent of the site’s readers visit five times or more, and 24 percent visit at least nine times monthly.

“We’re trying to build awareness on both the brand and consumer side,” said Tibbits. “We’ve shown people our logo, and they didn’t realize they knew us. We’re the biggest brand no one’s heard of.”